The long-term goal of this project is to define basic mechanisms of autoimmunity in Systemic Lupus Erythematosus (SLE), by focusing on disease-relevant T helper (Th) cells that induce the production of pathogenic anti-DNA autoantibodies in SLE. The full spectrum of major peptide epitopes, including naturally processed peptide epitopes, for the pathogenic autoantibody-inducing Th cells of human lupus that recognize nucleosomes in a promiscuous manner will be defined. Shared epitopes for autoimmune B-cells of lupus will also be identified. Immunologic relevance of the epitopes in influencing autoimmune T- and B-cell functions will be studied. T-cell receptor (TCR) and MHC-contact residues in the peptide epitopes will be finely mapped for finding consensus motifs that could lead to autoantigen -specific therapy of lupus in humans using tolerogenic peptides or altered peptide ligands. Altered peptide ligands that are partial agonists or antagonists will be designed and studied for blocking pathogenic anti-DNA autoantibody production in vitro. Nucleosomal peptide-HLA-DR tetramers (or peptide-MHC-Ig chimeric dimers) will be made to track autoimmune T-cells in lupus patients and family members for diagnostic and prognostic purposes, and for studying the effects of peptide tolerogens in vitro. The second part of the project will deal with mechanisms of prolonged hyper-expression of CD40 ligand (CD40L) and resistance to anergy induction and maintenance in T-cells of human lupus. Major components of T-cell signal transduction pathways involved in T-cell activation, and anergy, particularly in the context of CD40L hyper-expression will be defined. The role of differential MAPK activity in CD40L hyper-expression and stability of CD40L mRNA in lupus T-cells will be studied. Possible anomalies in B7-CD28, and CTLA-4 expression and function in lupus T-cells that could lead to the above mentioned defects being analyzed. Identification of critical peptide epitopes for the autoimmune T helper cells of lupus and studies on regulatory defects in expression of co-stimulatory signaling molecules are leading towards an understanding of basic mechanisms of the disease and development of specific immunotherapy.